Varactor tuned flexible interventional receiver coils

Abstract

The tuning of an interventional receiver coil for magnetic resonance imaging signals is tuned by coupling a varactor tuned circuit with the coil and adjusting a DC voltage applied to the varactor to alter the tuning whereby the coil is tuned to the Larmor frequency of the MRI signals.

What is claimed is:  
     
         1 . A receiver for interventional MRI signal detection comprising: 
 a) a coil for placement interventionally for detecting MRI signals, and    b) a tunable circuit connected with the coil for tuning, the tunable circuit including a varactor and a voltage source for applying a bias voltage to the varactor for controlling capacitance thereof and thereby enhancing signal reception.    
     
     
         2 . The receiver as defined by  claim 1  wherein the varactor is connected in parallel with a fixed capacitor to form a parallel capacitor circuit, the parallel capacitor circuit being serially connected between the coil and an output port.  
     
     
         3 . The receiver as defined by  claim 2  wherein the voltage source comprises a digital to analog converter controlled by a computer.  
     
     
         4 . The receiver as defined by  claim 2  wherein the voltage source comprises a DC voltage source connected with a variable potentiometer.  
     
     
         5 . The receiver as defined by  claim 2  and further including a diode connected across the output port for Q-spoiling and a DC blocking capacitor serially coupling the tunable circuit to the output port.  
     
     
         6 . The receiver as defined by  claim 1  and further including a diode connected across the output port for Q-spoiling and a DC blocking capacitor serially coupling the tunable circuit to the output port.  
     
     
         7 . The receiver as defined by  claim 6  wherein the coil is a flexible coil which can assume a plurality of configurations.  
     
     
         8 . The receiver as defined by  claim 1  wherein the coils is a flexible coil which can assume a plurality of configuration.  
     
     
         9 . A method of tuning an MRI signal receiver coil comprising the steps of connecting a tunable circuit including a varactor with the coil and varying the capacitance of the varactor.  
     
     
         10 . The method as defined by  claim 9  wherein the step of varying the capacitance of the varactor includes varying DC voltage across the varactor.  
     
     
         11 . The method as defined by  claim 10  wherein the DC voltage is varied manually with a potentiometer.  
     
     
         12 . The method as defined by  claim 10  wherein the DC voltage is varied automatically with a microcontroller controlling a digital-to-analog converter.  
     
     
         13 . The method as defined by  claim 12  wherein the microcontroller controls the digital-to-analog converter in response to a phase comparison of a voltage across a reference capacitor.